Intravenous (IV) administration of fluids and drugs is an integral part of the routine care of patients, especially those undergoing anesthesia and surgery. Every year in the United States, some 20 million patients undergo surgery and anesthesia. IV infusion is essential as a route of drug administration during induction and maintenance of anesthesia throughout surgical or other procedures.
During administration of anesthesia, invariably there is a need for administration of IV fluids using variable flow rates. In addition to providing a basal infusion rate (maintenance IV fluids), there is a need for frequent intravenous administration of different anesthetic or other medications in boluses. While it is important that these medications are carried into the cannulated vein by a continuous IV flow, administration of excess quantities of IV fluids is frequently undesirable, or deleterious. It follows that a moderately slow and flow-adjustable IV delivery system is preferred. However, ongoing blood or intravascular volume losses, or cardiovascular instability due to occasionally profound general or regional anesthesia, allergic reactions or intravascular volume redistribution, can create the need for quick delivery of larger fluid boluses or faster infusion rates in order to support the circulation. Fluid loading or replacements are frequently administered with great immediacy during various surgical or interventional procedures.
The most commonly used IV infusion system consists of a bag filled with IV fluids, a drip chamber, roller clamp (variable resistance controller) for control of the flow and tubing connected to an IV catheter. The elevated IV bag in this system serves as a pressure source, the roller clamp as a user-controlled resistor, and the IV catheter as a fixed resistor.
Most commonly, the rate of IV fluids flow is determined by the rate at which drops of liquid are observed falling through a drip chamber. Gravity infusion of the parenteral solution is accomplished by suspending the solution container several feet above the patient and connecting the solution container to the venopuncture site via a disposable intravenous administration set which includes a drip chamber and flexible delivery tube.
Flow rates (drops/ml/min) are controlled by use of a roller clamp. U.S. Pat. No. 4,175,558 describes a roller clamp for collapsing the delivery tube to control the flow rate. The roller clamp is a simple, inexpensive, two-piece plastic device that progressively compresses the plastic tube of the intravenous administration set at a single point on the tube thereby occluding the tube to create a pressure drop across the restriction and a corresponding reduction in flow rate. Although the constancy of flow rates during use of such roller clamps is problematic due to cold flow or creep of the plastic tubing at the point of restriction, which causes the flow rate to decrease after setting, this problem is of negligible clinical importance in anesthesia practice. This is so, because the anesthesia provider by the nature of the profession repeatedly has to check and adjust the flow rate according to the clinical circumstances or phases of the anesthetic course.
Continuous flow through the infusion system is usually necessary to ensure the proper delivery of the injected drugs into the patient and avoid accumulation of repeated doses within the IV tubing. However, administration of excess IV fluids is undesirable and frequently harmful. Even in otherwise healthy patients, inadvertently administered large volumes of IV fluids can result in urinary bladder distention and need for urethral catheterization during the surgery, or urinary obstruction post-operatively, all of which can cause delays in discharge. In patients with heart or lung disease, the administration of excessive fluid volumes is a frequent cause of postoperative lung and cardiovascular dysfunction. This can result in congestive heart failure, pulmonary edema (swelling of the lungs) and difficulties in discontinuing mechanical ventilation (breathing machine) after surgery and anesthesia.
While the administration of IV fluids is commonly controlled using "microdrip" IV infusion systems (60 drops/ml), which provide reliably slow infusion rates, these systems are not suitable for administration of fluid boluses and emergent intravascular expansion or replacement of ongoing surgical volume losses should that become necessary (blood loss, syncope, allergic reaction to medications or contrast agents, etc.) during the procedure.
On the other hand, the macro-drip infusion systems (15 drops/ml), which are most commonly used in anesthesia, allow for administration of high fluid rates and fluid boluses, but controlling the flow rate is cumbersome and inexact. Since these systems are capable of delivering high flow rates, failure to frequently assess and adjust the infusion rate using a roller clamp can easily result in administration of excess IV fluids, i.e., 1000 ml over 10 min. The risk of administering large fluid volumes is ever present also due to the deficiencies inherent in these infusion systems. For instance, the rate of drip formation has been found to be an inaccurate measure of flow rate because of the influence of temperature, fluid composition, orifice diameter, and orifice shape. Furthermore, the cold flow (creep) in the tubing underlying the roller clamp contributes to flow variation in excess of 15% over 45 minutes. When a vein collapses, critically high flow velocities occurs, causing the distention of the vessels (produced by the downstream resistance) and paradoxically increase in the IV flow. Veins are characterized by an opening pressure and by a small resistance to flow. Tissues behave as ordinary resistors with a resistance higher than that of veins. The opening pressure of tissue usually is no greater than that of veins, at least initially. In tissues, there is no obstructing pressure when there is no extravasation. However, as fluid is infused, opening tissue pressure rises. In response to these changes in flow rates, the clinician frequently has to check and adjust the roller clamp in order to properly adjust the IV flow so that the flow is continuous, keeping the veins open and assuring the delivery of administered medications and anesthetics, but not excessive to result in fluid overload or infusion of inappropriately large quantities of IV fluids.
In addition to the mentioned irregularities in maintaining the steady flow rate, many clinical situations produce venous collapse, resulting in veins and surrounding tissues behaving like Starling resistors and influencing the flow rate. Typical situations include patient positioning, blood pressure cuff inflation, venous tourniquets (or strapping of the patient's arm to an operating table on-board extension), problematic venous sites, catheter against the venous wall, etc. The clinician is unaware of actual resistance provided by the roller clamp. He or she simply moves the roller clamp until proper flow rate is reached (judged by measuring the rate of drop formation).
Thus, when the IV flow ceases in the above situations, the dripping in the chamber also stops. The clinician frequently completely opens the roller clamp in an attempt to restore the IV flow. However, since deflation of the blood cuff, removal of the tourniquet, or patient repositioning restores the flow, so that unless the clinician remembers that he or she intentionally opened the roller clamp and fails to detect restoration of flow in a timely manner, the patient will almost certainly receive a large bolus of fluids. Since the most commonly used IV set in anesthesia, 15 drops/ml ("macrodrip"), is capable of delivering flow rates as high as 75 ml/min through a 20 G (gauge) IV with just a moderate elevation of the IV bag, this situation would result in administration of 750 ml of fluids in just 10 minutes.
Frequent adjustment in the flow rate is important to counteract periodic, potentially large changes in IV flow due to the described interference in which the flow can start and stop even with small changes in bag elevation or patient repositioning. Thus, the administrator is frequently tempted to completely open the roller clamp during the times when the infusion rate is slowed or when there is a need for "flushing" of administered medications or anesthetics into the IV tubing. Failure to notice the increase in flow when the obstruction to the flow is removed, or failure to decrease the flow after the administered medications are flushed, can again, easily result in administration of excess of fluids. This readily occurs during the times when the clinician becomes distracted by performing a procedure or administering anesthesia.
IV systems used in anesthesia and during different procedures (i.e. cardiac catheterization, interventional radiology, GI and pulmonary endoscopies, etc.) are also frequently used as a carrier for administration of sedatives, anesthetics and other medications. Most commonly, drugs are administered from a syringe with the needle into the flowing IV stream that is powered with gravity. Although administration of IV fluids per se may not be needed or even might be undesirable, IV administration of medications requires a free flowing IV stream, which necessarily results in fluids being administered to the patient.
While using a microdrip IV set (60 drops/ml) for this purpose would minimize the possibility of inadvertent administration of large quantities of IV fluids and assure the delivery of injected medications by a slow IV flow, the maximum flow rate through this system is inadequate should the patient become unstable or require emergent IV intervention. On the other hand, macrodrip sets (15 drops/ml) are excellent for resuscitation, but carry the risk of inadvertent infusion of large IV boluses in the above described circumstances. Although theoretically, one can exchange the microdrip system for a macrodrip system if that becomes necessary, this is time consuming since this would be done in urgent situations. Additionally, exchanging the IV sets carries a risk of loosing the existing IV line, should the IV catheter inadvertently become dislodged during the maneuver, which occasionally happens clinically.
Systems for administering intravenous liquids are described in U.S. Pat. No. 3,298,367 and U.S. Pat. No. 5,318,515. The '367 patent describes a plurality of separate flow paths with each flow path having a predetermined flow characteristic. Each path is associated with an on/off element. An even more sophisticated system for administering intravenous fluids is described in the '515 patent. The '515 patent describes a plurality of separate flow paths with each flow path having a predetermined flow characteristic. The flow in each path is controlled by a selector mounted to a housing which allows for setting or selecting a desired flow rate.
In the dynamic environment during operation and delivery of anesthesia, the administration of fluids using the systems described in both the '367 and '515 patents would require a time consuming selection from a finite number of tubes and associated flow characteristics.
Canadian Patent No. 1,125,134 describes an apparatus for administering incompatible I.V. liquids. The '134 apparatus includes two independent parenteral solution chambers with two independent piercing pin assemblies and two independent sight-drip chambers for incompatible liquids. Hence, the user of the '134 system would be required to insert two separate piercing spikes into two separate solution containers. In addition to adding complexity to administering IV fluids, this system is by necessity costlier since two bags with IV fluids are used. Additionally, since these two piercing spikes are separately inserted, they are frequently positioned at different levels above the infusion site. This, in return, results in different gravity driving pressure and can result in difficulty in maintaining a simultaneous flow through both IV paths, or over-spilling of fluids or medications from one path to another. By having the drip chambers in a common enclosure, the present invention prevents these problems.
Several flow rate regulators, such as the Abbott Laboratories' Dial-A-Flow, see U.S. Pat. No. 3,877,428 have been introduced in recent years in attempts to overcome the aforementioned disadvantages associated with the use of conventional roller clamps and infusion procedures. U.S. Pat. No. 5,019,055 is yet another invention designed in order to improve the accuracy of delivering the desired flow rate and is said to represent an advantage of the aforementioned Dial-A-Flow device.
However, since anesthesia providers routinely work in an intense and dynamic environment prone to human mistakes, any unnecessary complexity of the equipment used during administration of anesthesia introduces a risk of a mishap. These systems are also designed to provide a wide range of flow rates through a single drip chamber. Since the capillary tube in this singular drip chamber has to be of a large diameter, this results in a very slow droplet formation when a slow infusion rate is selected. This again, precludes monitoring of the flow rate and prevents the operator from assuring continuous flow by observing the rate of drops formation, which is the most common and convenient method of monitoring of IV flow used by anesthesiologists. The ability to observe flow rate and adjust it accordingly is far more important in anesthesia practice than the limitation of flow provided by these infusion devices. Consequently, none of these devices have been widely accepted in anesthesia practice. Thus, the present invention also provides a means of avoiding the mixing or flow from one path to another by having separate drip chambers and flow paths at the same height in one enclosure.
It is an object of the present invention to provide an infusion system that corresponds to the conventional droplet monitoring technique and will, therefore, be acceptable to medical practitioners.
Another object of the invention is to provide an infusion system that permits the user to quickly and easily adjust flow rates in accordance with the observed clinical response of the patient receiving the fluids.
Another object of the invention is to provide an infusion system that is inexpensive to manufacture.
Another object of the invention is to provide a sterilized kit containing an infusion system for the administration of intravenous fluids.
Another object of the invention is to provide a simple and easy method for administration of intravenous fluid.